Background: Several markers have been discovered and validated for alopecia areata (AA). However, their exact roles have not yet been fully studied. Erythroid differentiation regulator 1 (Erdr1), an IL-18-regulated factor, is one of these novel markers. Objectives: This work aimed to study the role of Erdr1 in AA and to correlate its skin mRNA expression level with serum level of IL-18. Methodology: Twenty-five AA patients and 10 healthy control subjects were included in the study. The level of skin expression of Erdr1 mRNA was measured by reverse transcriptase-polymerase chain reaction (RT-PCR). Serum IL-18 level was measured by enzyme-linked immunosorbent assay (ELISA). Results: The level of skin expression of Erdr1 mRNA was 0.214 fold lower in AA patients compared to control group, it was (in log relative unit) 6.61 ± 0.188 Vs 7.17 ± 0.193 for AA patients Vs control group respectively. The level of IL-18 (in pg/ml) in serum was higher in AA patients compared to control group, it was 245.1 ± 51.8 Vs 96.8 ± 38.1 for AA patients Vs control group respectively. In severe type of the disease, there was lower skin level of Erdr1 mRNA and higher serum IL-18 level than in moderate one. There was a significant negative correlation between IL-18 serum level and Erdr1 mRNA skin expression level among patients group (r= -0.786, P <0.001). In conclusion: Erdr1 has a role in the pathogenesis of AA and can be used as a marker for diagnosis.